Galaxy cluster Abell 370 contains an astounding assortment of several hundred galaxies tied together by the mutual pull of gravity. The brightest and largest galaxies in the cluster are the yellow-white, massive, elliptical galaxies containing many hundreds of billions of stars each. Spiral galaxies — like our Milky Way — have younger populations of stars and are bluish.
Entangled among the galaxies are mysterious-looking arcs of blue light
– distorted images of remote galaxies behind the cluster. These
far-flung galaxies are too faint for Hubble to see directly. Instead,
the cluster acts as a huge lens in space that magnifies and stretches
images of background galaxies like a funhouse mirror. The massive
gravitational field of the foreground cluster produces this
phenomenon. The collective gravity of all the stars and other matter
trapped inside the cluster warps space and affects light traveling
through the cluster, toward Earth.